Compositions containing a bisphenol A-type epoxy resin excellent in adhesiveness or mechanical strength, an epoxy resin free from UV absorption, for example, a hydrogenated bisphenol A-type epoxy resin or an alicyclic epoxy resin, a curing agent, and a curing catalyst are frequently used as resin compositions for optical semiconductor device sealing. Such compositions, however, disadvantageously cause change in color or cracks due to light, heat, or the like from LED devices, as the luminance and output of the LED devices are increased.
To solve these problems, a resin containing one or more epoxy groups introduced in a silicone resin that offers a UV absorption-free and flexible cured article is known. For example, a silicone resin having one or more cyclic ether-containing groups such as a glycidyl group and an epoxycyclohexyl group (Patent Literature 1), a reaction product of epoxyalkoxysilane and silanol (Patent Literature 2), and an alicyclic epoxy-modified silicone resin used in combination with an alicyclic epoxy resin (Patent Literature 3) are known. Silicone resins, however, have very high gas permeability as compared with epoxy resins. Therefore, products having a higher silicone content are more difficult to use in usage required to have low gas permeability. Accordingly, an addition reaction-type phenyl silicone resin composition is disclosed as a resin composition having low gas permeability (Patent Literature 4), but is still unsatisfactory in terms of low gas permeability and adhesiveness.